A body starts from rest with uniform acceleration. If its velocity after n second is v, then its displacement in the last two seconds is

∵v=0+na⇒a=v/n Now, distance travelled in n sec α⇒Sn=12an2 and distance travelledin (n−2)sec⇒Sn−2=12a(n−2)2∴Distance travelled in last two seconds,=Sn−Sn−2=12an2−12a(n−2)2=a2n2−(n−2)2=a2[n+(n−2)][n−(n−2)]=a(2n−2)=vn(2n−2)=2v(n−1)n